The invention relates to a rotational direction indicator for an electric motor, to an electric motor and to a pump assembly.
Electric motors are regularly to be operated in a preferred rotational direction, wherein the rotational direction is directed to the application purpose of the apparatus driven by the electric motor. This for example is of particular relevance with centrifugal pumps which are driven by a three-phase a.c. motor. If the pump is operated in the wrong rotational direction, this results in a significantly reduced pump efficiency. An operation of the electric motor in the wrong rotational direction, for example with a three phase a.c. motor, may originate from an unintended commutation of two phases on connection to a voltage supply.
It is therefore necessary on connection of an electric motor, to control whether the rotational direction of the electric motor corresponds to the envisaged rotational direction. A signal device for signaling a wrong rotational direction of an electric motor is known for example from the document DT 25 32 436 A1. A signal device is disclosed in this, which is arranged on a cooling fan, within a fan housing. With regard to the signal device, a movable tongue is moved by the airflow of the cooling fan into the fan wheel, given the wrong rotational direction of the electric motor. There, the tongue is hit by the blades of the fan wheel and causes a rattling noise which signalizes a wrong rotational direction.
The tongue of such a signal device disadvantageously is subjected to a large wear, when this is hit by the fan wheel. Furthermore, such a signal device only provides an acoustic signal. For example, a rotational control is difficult with this in noisy surroundings. It is further disadvantageous, that the correct rotational direction is set in a fixed manner with regard to the signal device. It is not possible to select the desired rotational direction in the individual case.